I have absolutely no idea what you're trying to say. The RPIT will be bound by the caller and there exists a type such that the declared trait is implemented. M

I have absolutely no idea what you're trying to say. The RPIT will be bound by the caller and there exists a type such that the declared trait is implemented. Meanwhile an impl parameter will be bound within the method with some type existing such that the trait is implemented. That is the implication of existential, "there exists a type such that...".